Color-tunable emission by adjusting sensitizer (Yb3+) and excitation power of 980 nm in NaGdTiO4: Yb3+/Tm3+/Er3+ phosphors for light emitting diodes

Color-tunable upconversion emission was explored in the NaGdTiO4 synthesized by a high temperature solid-state reaction process. NaGdTiO4: Er3+, NaGdTiO4: Yb3+/Tm3+ and NaGdTiO4: Yb3+/Er3+ are mainly dominated by green, blue and yellow light emissions under 980 nm diode laser, respectively. The intensity ratios of red to green luminescence and blue to green luminescence increase with increasing the concentration of Yb3+ in NaGdTiO4: Yb3+/Tm3+/Er3+ phosphors. Changing the power of laser can influence the photon transfer pathways and eventually tune the emission colors. Additionally, the laser excitation heating effect and the temperature dependent spectra were also investigated, which indicated that the laser-induced heating effect was not the main reason for the laser power to change the emission. The CIE chromaticity coordinates of NaGdTiO4: 60% Yb3+/1% Tm3+/5% Er3+ are close to the standard white light (x = 0.33, y = 0.33) and the sample has a good thermal stability. The strategies for color tuning of upconversion emission proposed in the NaGdTiO4 would be beneficial to achieve efficient multicolor (including white light) luminescence.